The invention relates to an operating circuit for a high-pressure gas discharge lamp. A particular problem of high-pressure gas discharge lamps consists in that they can usually be ignited only in a cold state, that is to say only after a certain cooling phase after the last operation.
The disadvantage that the lamp cannot be used during this period, which can take approximately 2 to 10 minutes, has led to the development of special hot igniters for high-pressure gas discharge lamps. However, a general application of these hot igniters is obstructed by the considerable technical outlay associated with them and the costs thereby occasioned.
A substantially simpler alternative consists in providing a second lamp, in general a simple incandescent lamp, which can bridge the cooling or dark phase. Of course, an attempt is made for the operating circuit of the high-pressure gas discharge lamp to switch in this incandescent lamp independently when an operator would like to switch on the high-pressure discharge lamp, but the latter cannot be ignited. It has been conventional to provide for this purpose a very complicated electronic system which detects the voltage drop across the high-pressure gas discharge lamp, reaches a conclusion on the burning state and switches in the incandescent lamp if required. An example is the Tridonic LRM 300 ignition-time bridging unit. This unit is estimated to contain between 50 and 80 electronic components and requires a volume of approximately 7.times.40.times.30 mm, specifically in each case exclusively for the ignition-time bridging function. This technical outlay and the costs and overall size associated therewith are regarded as being very disadvantageous.